Stored energy thrust termination device



Sept. 15,1970 WE VER ETAL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 5Sheets-Sheet 1 1 INVENTOR. Robert B. Weaver BY Stuart E. WeaverAttorneys Sept. 15, 1970 R. B. WEAVER ET AL 3,523,249"

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 '5Sheets-Sheet :2

INVENTOR. Robert B. Weaver Stuart E. We ver BY Attorneys Sept. 15, 1970R. B. WEAVER ET AL 3,528,249

STORED ENERGY THRUSI TERMINATION DEVICE Filed May 29, .1968

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Sept. 15 1970 WEAVER ET AL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 5Sheets-Sheet 4 INVENTOR- Robert B. Weaver BY Stuart Weaver I f AttorneysSept. 15, 1970 R. B. WEAVER ETAL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 I 5Sheets-Sheet 5 COMBINED LOAD FROM TENSION BAND 5 SPRINGS sooow POINT c gPOINT B ,5 POINT A ts LOAD FROM SPRINGS ONLY :5 LOAD REou/R 8 2000 TOMOVE CUT ER v \\--?L0AD FROM TENSION BAND ONLY D 3 2 looo- Q C I I I I ll I .05" lo" '5" 20" 25" 30" Cutter Travel Radially Inward -|ooo- Fig.13

attorneys United States Patent 011?? 3,528,249 Patented Sept. 15,, I9703,528,249 STORED ENERGY THRUST TERMINATION DEVICE Robert B. Weaver, PaloAlto, and Stuart E. Weaver, Los Angeles, Calif., assignors to WeaverAssociates, Inc-, Palo Alto, Calif., a corporation of California FiledMay 29, 1968, Ser. No. 732,954 Int. Cl. F021; 9/04 US. Cl. 60254 11Claims ABSTRACT OF THE DISCLOSURE A device for terminating the thrust onan accidentally ignited solid propellant rocket including metal bandswhich encompass the rocket casing to retard expansion of it duringpressure built-up within the casing caused by burning of its solidpropellant. Coupled to the encompassing bands are rupturing means whichare actuated by the build-up of tension in the band to cause alongitudinal cutter to penetrate the casing thus rupturing it. Thecutter is driven by the combination of stored energy from two pairs ofBelleville springs and the tension in the bands. The springs are coupledto the cutter by oilcenter toggle struts; these are located at an angleto the casing to provide a bias or lockout force Which preventsaccidental triggering. Thus, before the spring force can move the cutterinto the casing the lookout force also provided by the springs must beovercome by the band tension.

BACKGROUND OF THE INVENTION This invention relates to a stored energythrust termination device and more particularly to a device for use withsolid propellant rocket motors.

In the utilization of solid propellant rocket motors, there is apossibility of accidental ignition during transportation, handling andstorage, or while in launch position during the preparation of a missilefor flight. This is especially critical with smaller rocket motors whichare used and carried by ground forces, for example, by truck. Possiblecauses of accidental ignition are fire, sparks, hot fragments,lightning, and inadvertent actuation of the igniter as, for example, bya collision of the rocket motor with another object or the ground.

Once ignited the propellant Will burn to exhaustion because there is noknown way of extinguishing the flame. Unless the thrust forces arecounteracted in some manner or the motor destroyed, an accidentallyignited rocket can cause damage and injury at a great distance from thepoint of the accident. If free flight should be obtained, populatedareas could easily be jeopardized.

One method of terminating thrust is disclosed and claimed in Pat.3,167,910 in the name of Robert B. Weaver, entitled Thrust TerminationDevice and Method and assigned to the present assignee. This utilizes aband encompasing the casing which is responsive to expansion of thecasing during pressure build-up, caused by an accidental ignition, totrigger a cutter which ruptures the casing rendering it harmless. In aspecific embodiment of this patent the force for the cutter is directlyobtained from the tension in the encompassing band. This method is veryeifective for types of rocket motors such as those for ballisticmissiles where there is appreciable circumferential growth of the rocketcasing. However, in the smaller tactical missiles which are, forexample, for ground use and are built for more rugged handling, thecasing is thicker in proportion to its diameter and therefore stressedlower. Thus, the amount of circumferential growth in relation to thesize of the casing is less to somewhat reduce the efliciency of the typeof thrust of termination device as shown in the above patent.

There is therefore a need for a thrust termination device which isespecially applicable and useful on the smaller tactical missiles.

OBJECTS AND SUMMARY OF INVENTION In general it is an object of thepresent invention to provide an improved thrust termination device inwhich propulsive hazards associated with the accidental ignition ofsolid propellant motors are eliminated.

Another object of the invention is to providea device as above which isespecially suitable for rocket motors having a relatively smallcircumferential growth.

It is another object of the invention to provide a device as above inwhich stored energy is utilized but in which the forces created byignition of the solid propellant rocket motor are utilized fortriggering this stored energy; and

Another object of the invention is to provide a device as above in whichthe force characteristic applied to the cutter which ruptures the rocketcasing is idealized.

In accordance with the above objects there is provided a device forterminating the thrust on an accidentally ignited solid-propellantrocket motor of the type having a casing, means encompassing the casingto retard expan sion of the casing during pressure build-up within thecasing caused by burning of the solid-propellant Within the casing, andmeans actuated by the encompassing means as it is expanded to rupturethe casing to thereby destroy the rocket motor. The improvement of thepresent invention comprises energy storage means and means responsive tothe encompassing means for releasing the stored energy of the energystorage means and coupling at least a portion of this energy to therupturing means to thereby aid in rupturing the casing.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view of the thrusttermination device embodying thepresent invention including the bandswhich encompass the rocket casing;

FIG. 2 is a plan view of an interlocking portion of the bands of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 2;

FIG. 4 is a plan view of FIG. 2 but in an unlocked or explodedcondition;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4;

FIG. 6 is a plan view, partially broken away, of the actual mechanism ofthe thrust termination device of the present invention with the topcover removed;

:FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 6;

FIG. 8 is a cross-sectional view similar to FIG. 7 but showing thecutting device in an extended position;

FIG. 9 is an elevational view taken along the line 9-9 of FIG. 6;

FIG. 10 is a cross-sectional view taken along the line 10-*10 of FIG. 6;

FIG. 11 is a cross-sectional view taken along the line 1111 of FIG. 6;

FIG. 12 is a cross-sectional view taken along the line 1212 of FIG. 6;and

FIG. 13 is a set of composite curves useful in understanding theoperation and theory of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1,there is shown the complete thrust termination device which includesencompassing band means 10 which are divided into the two halves 10a and10b which would normally encompass or be locked to a rocket casing (notshown). The axis of the rocket 3 would of course be vertical withrelation to the drawing. The rupturing device itself is shown at 11 withbands 10a and 10b having one of their free ends coupled to each side ofit. The other end of the bands are tied together by coupling means 12which is shown in greater detail in FIGS. 2 through 5.

Referring now more specifically to these figures, in FIGS. 2 and 3 thecoupling means are shown in a locked position and in FIGS. 4 and 5 anopen position ready to 'be placed around the circumference of a rocketmotor casing. Band halves a and 10b include at their end terminationslocking sections 13 and 14, which are oppositely oriented with respectto each other and mesh as shown in FIG. 3. The section 14 carriesthereon a threaded stud 16 with a knurled fastening knob 17. This slidesinto a cutout 18 in section 13 to provide a permanent fastening afterinterlocking of the sections 13 and 14. A bar 19 is mounted on section13 (the bar also being shown in FIG. 1) and has a cutout portion 21 toallow passage of knob 17. The bar serves to re-enforce the coupling 12and also to provide protection for knob 17 and stud 16 to preventagainst accidental opening of the coupling.

The rupturing means which are actuated by the tension in bands 10a and10b for rupturing a rocket casing to terminate thrust is best showngenerally in FIG. 6 where the individual bands 10 are mounted onupstanding wall portions 23 and 24 which are mounted and welded to abase 26. The base which is best shown in FIG. 9 has a curved concavebottom surface to fit a particular rocket casing. A cover 27 protectsthe entire mechanism of the rupturing device. This cover is, however,removed in FIG. 6. Four compression springs 28a, b and 29a, b aremounted on walls 24 and 23, respectively to provide the stored energyfor powering the cutter of the thrust termination device. These arecompression springs of the Belleville type. Each individual spring ismade of four single Belleville discs stacked in series and eightparallel pairs of two stacked in series. The maximum output of eachindividual spring is 3,000 pounds. This is applied through respectivecoupling plates 31 and 32 to the cutter means in a direction parallel tothe axis of the actual rocket motor. FIGS. 7 and 8 show the couplingplates each of which include horizontally extending ram portions 33 and34 respectively which are suspended between abutments 36 and 37 in thecase of ram 33 and abutments 38 and 39 in the case of ram 34. Needlebearings 41 allow for free longitudinal or horizontal movement of therams. Belleville springs 28a, b and 29a, b all include spring guidemeans 42 which are in the form of rods fitted through the individualrespective walls 23 and 24 to protect against accidental sliding of oneof the spring discs out of the spring. Although Belleville type springshave been shown in the preferred embodiment other springs may be used.

FIG. 7 illustrates the bladed cutter 43 of the present invention in afirst or retracted position with springs 28 and 29 in a stored energyposition. FIG. 8 shows cutter 43 in a fully extended position as itwould be when the rocket casing was fully ruptured with the storedenergy of springs 28 and 29 expended and the spring expanded.

Cutter 43 as shown in its first position in FIG. 7 includes a shankportion 44 having upwardly extending fingers 46 through which a pin 47extends. Pin 47 is maintained in place by abutments 48 and 49 whichextend from blocks 36 and 38 respectively. As will be explained below,downward force is applied to cutter 43 by means of pin 47. Shank 44includes shear pins 50 and 51 extending through the shank and, as bestshown in FIG. 12, each shear pin includes an end designated with thesuffix a, for example 49a, which extends into mounting block 52 which ismounted to base 26. Block 52 includes a key-way 53 in which the cutter43 is guided downwardly.

The energy storage means which are, of course, the Belleville springs28a, b and 29a, b are coupled to the rupturing means which includecutter 43 by means of two toggle struts 56 and 57. In their firstposition, as shown in FIG. 7, they are in a compressed condition due tothe force of ram 33 which produces forces on the strut in the directionof arrows 58 and 59. Struts 56 and 57 include rounded ends which areadapted to mesh with the open V construction 33a and 44a of the ram 33and shank 44. The struts 5'6 and 57 in their first position, as shown inFIG. 7 are set at an approximate angle of 3 /2 with respect to thehorizontal. Thus, the resulting forces on the cutter 43 are in thedirections as shown by arrows 58 and 59; force 59, the major force, ishorizontal and force 58 is vertical. These two force vectors areessentially the components of the force delivered by rams 33 and 34 asindicated by the arrows. Because of the upward 3 /2 cant of struts 56and 57, force 58 is in a direction away from the rocket casing to thusprevent accidental triggering of the cutter 43. Upward force 58 is afunction of the tangent of the angle the struts make with thehorizontal. Thus, for example, with a 3 /2 angle and a 3,000 pound forcein each separate spring each ram 33 and 34 will produce a 6,000 poundforce. Multiplied by the tangent of 3 /2" this yields an individualupward force of 366 pounds or a combined force of 732 pounds. Therefore,the cutter 43 cannot be moved until at least a 732 pound force overcomesthe spring force. Thus, for example, if the cutter itself has a weightof only 3 ounces the shock required to move the cutter would have to bein exces of 3,700g. The shear pins 49 and 51 provide an additionalsafety factor, which along with associated friction raises the force tomove cutter 43 from its first or stored energy position to approximately1,000 pounds.

The 3 /2 cant or angle of the struts away from the rocket casing isbelieved to be the ideal angle. If the angle is less than 2 then thedevice is susceptible to accidental triggering; on the other hand, anangle of greater than 6 would require a release force to be supplied bythe bands which would be excessive.

As best shown in FIGS. 11 and 12, the bands 10a and 10b, when placed insufficient tension, to provide a triggering force to overcome the above1,000 pound force to move struts 56 and 57 over-center (that is througha horizontal position) to allow the spring force to move cutter 43downwardly into the rocket casing to thereby rupture it. This tension isapplied substantially through band half 10a which is coupled to pin 47of cutter 43 through a series of levers. These levers are best shown inFIG. 12 where the band 10a is coupled to a band attach link 61 by a pin62. Link 61 is pivoted on an abutment 63 on base 26 to force a cutterdrive rocker arm 64 to rotate in a clockwise direction to move cutter 43downwardly. Specifically, link 64 includes a left end 64a which is incontact with link 61 and a right end 64b which meshes with fingers 46 ofcutter 43 into contact with pin 47. Link 64 is pivoted on a pin 66 whichin turn is mounted on a link 67 which is pivoted to base 26 by a pin 68.The purpose of link 67 is to allow movement of link 64 toward the cutter43 as it moves the cutter downwardly. Link 61 is pivotally attached tobase 26 through links (see FIG. 6) which couple to blocks 52' mounted onthe base.

Band half 10b is coupled to the other side of cutter mechanism 11 by alink 69 which includes a tongue 70 which slides within a U-shaped groove71 cut into block 52. The extend of the protrusion of tongue 70 intogroove 71 is adjusted by means of a screw 72 best shown in FIG. 6 which,carries V-shaped wedges 73 and 74 which space the link 69 from the base26 (see also FIG. 12). Wedges 73 and 74 are extensions of collars 76 and77 which are carried by screw 72. The collars are oppositely threaded toallow opposite movement toward each other or away from each other whenscrew 72 is rotated to thus adjust the tension in the band 10. The screw72 is rotated through a ratchet block assembly 78 which in turn isturned by a wrench 79 having a shear pin 81.

The ratchet block is manufactured so as to have a maximum torque of 60inch pounds. The shear pin 81 of wrench 79 has a shear torque of 70 inchpounds to serve as a backup in case of failure of the ratchet blockrelease. Thus, accidental triggering by over-tightening of the band isprevented.

The specific construction of 'band 10, as best shown in FIGS. 11 and 12,includes a multiple-layer construction for flexibility and to allow forsliding friction. Specifically, as is shown in FIG. 11 themultiple-layer band includes as its load carrying portion two stainlesssteel bands 81 and 82 which are welded to opposite sides of a shank 83mounted by pin 62 to base 26. A band 84 is adjacent to band 83 and isnonloaded. On its outer surface which is in contact with band 82 it iscoated with Teflon in order to provide sliding friction between itselfand band 82. On its inner surface it has bonded to it neoprene withTeflon impregnated glass cloth. The Teflon provides for sliding frictionbetween the load band layers and the rocket casing. Surrounding theentire band is a rubber outer coating 86. Thus, with the above bandconstruction the load bands 81 and 82 may move freely over the outerTeflon coating of band 84 to minimize friction between the load bandsand the rocket casing.

The cutter assembly 11 is basically constructed of stainless steel whichhas been hardened by precipitation methods to have a pH of 17-4. It iscorrosion resistant and in the hardening process it has its distortionreduced to zero.

OPERATION The curves of FIG. 13 will be used in explaining the operationof the present invention. Initially, the band halves a, 10b are fastenedaround the rocket casing by means of the coupling 12, as shown in FIGS.2 and 4. The band is then preloaded by, as shown in FIG. 6, the rotationof wrench 79 until the ratchet 78 begins to slip at a predeterminedtorque.

The thrust determination device is now ready to come into action if therocket should accidentally ignite. Upon accidental ignition the rocketcasing expands placing a load on the band which is applied to themechanism at band half 10a. The curve labeled load from tension bandonly shows the downward load on cutter 13 which is applied as best shownin FIG. 12 on pin 47 through the intermediate links 64 and 61. Thiscurve is shown as dashed line since it is a theoretical curve only. Ifthis were the only force on the cutter 43 it would naturally reduce asthe cutter traveled radially inward as. shown by the horizontal axissince the tension on the band Would be relieved.

Initially, the curve labeled load from springs only is at a negativevalue due to the shear pins and the upward force produced by struts 56and 57. After the cutter travels through its center position this loadbecomes positive, meaning radially inwards toward the rocket casing. Thecurve labeled combined load from tension band and springs is the actualload on the cutter 43 which is a combination of the load from tensionband only curve and the load from springs only curve. Note that at zerocutter travel the combined load curve is, of course, less than thedownward force contributed by the tension hand because of the negativespring load which provides the stored energy lock-out feature of thepresent invention.

The last curve shown is labeled load required to move cutter which isexperimentally determined by loading the cutter with a hydraulic ram andmeasuring the cutter movement as the ram pressure increases. The initialpart of the curve where cutter movement is small represents the forcerequired for deflection of the rocket casing before puncture and themore linear portion of the curve is the force required as the cutter ispenetrating the rocket casing. This curve neglects the shear pin forcewhich, of course, is an added safety feature. Thus, in operation, tohave movement of the cutter the combined load curve must always exceedthe load required curve. For example, note that cutter movement wouldstop at point A absent the spring force. Similarly, springs alone wouldnot force the cutter to rupture the casing since at any cutter movementto the left of point B the springs do not produce a suflicient force.Point C indicates the actual case rupture point where the cutter hasproduced a crack long enough to allow a longitudinal rupture of therocket casing.

Note that the load from springs only curve increases with increasingcutter travel even though the Spring force is decreasing as the springsexpand. This is because the downward force is a function of the tangentof the angle that the toggle strut makes with the casing and thistangent function is, of course extremely non-linear. Thus, the decreasein spring force is more than compensated for.

In summary, therefore the present invention provides an improved thrusttermination device which is especially useful on smaller tacticalmissiles since it utilizes combined characteristics of the tension inthe bands surrounding the rockets and the stored energy of springs toprovide for the proper force characteristic for rupturing the rocketcasing. By use of the canted toggle strut construc tion accidentaltriggering of the stored energy is prevented even under extremeconditions. This is especially valuable when the tactical rocket isbeing transported over rough terrain or is subject to being dropped fromits carrying vehicle.

We claim:

1. A device for terminating the thrust on an accidentally ignitedsolid-propellant rocket motor of the type having a casing, meansencompassing the casing to retard expansion of the casing duringpressure build-up within the casing caused by burning of the solidpropellant within the casing, and means actuated by the encompassingmeans as it is expanded to rupture the casing to thereby destroy therocket motor, wherein the improvement comprises, energy storage means,and means responsive to said encompassing means for releasing the storedenergy of said energy storage means and coupling at least a portion ofsaid stored energy to said rupturing means to thereby aid in rupturingsaid casing.

2. A device for terminating the thrust on an accidentally ignitedsolid-propellant rocket motor of the type having a casing, meansencompassing the casing to retard expansion of the casing duringpressure build-up within the casing caused by burning of the solidpropellant within the casing, and means actuated by the encompassingmeans as it is expanded to rupture the casing to thereby destroy therocket motor, wherein the improvement comprises, energy storage meansfor providing a predetermined force, and means coupling said storagemeans to said rupturing means, said coupling means having a firstposition for coupling a component of said predetermined force to saidrupturing means which is in a direction away from said casing and asecond position for coupling a component of said predetermined force tosaid rupturing means in a direction toward said casing to thereby aid inrupturing said casing.

3. A device as in claim 2 in which said energy storage means areBelleville type springs.

4. A device as in claim 2 in which said predetermined force is exertedin a direction parallel to said casing.

5. A device as in claim 2 in which said coupling means includes a togglestrut disposed at a predetermined angle away from said casing in saidfirst position.

6. A device as in claim 5 in which the amount of force transmitted bysaid strut to said rupturing means varies non-linearly with respect tothe angle formed between said strut and easing.

7. A device as in claim 6 in which said non-linear relation is a tangentfunction of said angle.

8. A device as in claim 7 in which said angle in said first position isbetween 2-6 degrees.

9. A device as in claim 2 in which said energy storage means include aram which has an end face with an open V configuration which couples tosaid coupling means and said rupturing means also includes an open Vportion which also couples to said coupling means.

10. A device as in claim 2 in Which said encompassing means include amultilayer band at least one of the layers being substantially a loadcarrying band and where another one of the layers carries substantiallyno load but is interfaced with a load carrying band by a substantiallyfrictionless surface.

11. A device as in claim 2 in which the force necessary to cause saidrupturing means to rupture said casing is a combination of a portion ofthe tension force in said encompassing means and a portion of saidpredetermined force contributed by said energy storage means.

References Cited UNITED STATES PATENTS 2,470,371 5/1949 Roessner 222-87XR 3,038,303 6/1962 Gose 60-254 3,167,910 2/1965 Weaver 60-254 XR3,295,324 1/ 1967 Conard et al. 60254 CARLTON R. CROYLE, PrimaryExaminer US. Cl. X.R.

